This is a tough one. You seem to have several barriers to overcome here.
How you deal with this really depends on how involved you want to get with your neighbor. If are in a place you plan on living for a long time and it appears your neighbor will as well then you may want to get more involved but if you are planning on moving soon you may just want to go through management.
If you live in a building with good management often they will have a resident mediation service, however this is fairly rare. To find out if they offer this service just ask to the property manager.
If your apartment does not have this service, you will need either to learn her language or bring in some sort of third party assistance. No matter how you proceed, you will need to prepare yourself before you meet with your neighbor.
Read the earlier post about dealing with your neighbor. Be clear about what is bothering you and remain calm. Have a plan for how you will proceed. You may want to do some research and see if anyone else has some solutions.
Remember what I said about getting involved? This may be out of your comfort zone, but knowing single moms myself, I know they would never turn down a good neighbor that would be willing to watch their child for a little bit from time to time
If you belong to a church or to some other social organization see if anyone speaks her language and would be willing to help you out.
Ultimately, it is going to take a group effort because of the barriers you have to overcome. Many times single moms just get so narrowly focused on what goes on inside their own walls because they just have too much to deal with. Additionally, a language barrier does not help anything. I have had plenty of neighbors that were just not very bright and that made things more difficult. Hopefully your neighbor is brighter than some of mine have been.
I hope this helps. If you don’t mind a slow paced resolution get to know her as best you can and invite her over for a cup of tea (coffee, soda, or even water works too) and talk as best as you can. Have her bring her child and you can get to know the tike at the same time and see how they interact. Often a change of scenery and activity will help a kid sleep better night. Additionally, this will give you the chance to see if the child has any developmental complications. This may not assist you in finding a solution but it will at least give you some insight into her world.
The bottom line is that you need your sleep and how you go about achieving this goal depends on your plan.
Please post back with an update if you have one.